Recently, in the vehicle industry, the demand for the durability, stability and fuel economy of vehicles is continuously increasing, and much effort is directed to satisfying the demand.
In particular, many attempts have been made to enhance the properties of rubber, as a material for vehicle tires, especially tire treads, which are in contact with roads. The rubber composition for a vehicle tire contains a conjugated diene-based polymer, such as polybutadiene or butadiene-styrene copolymer.
Thorough research is currently ongoing into the addition of various reinforcing agents to conjugated diene-based rubber compositions to increase the performance of vehicle tires. Specifically, as vehicles are required to exhibit stability, durability and fuel economy, rubber having high wet skid resistance and mechanical strength and low rolling resistance is being developed as material for vehicle tires, especially tire treads, which are in contact with roads.
In this regard, rubber compositions having superior fuel economy and wet grip are under study, as disclosed in Japanese Patent Application Publication No. 2013-139491, but the effects thereof are still insufficient.